Acupuncture is increasingly used by the American Public for the treatment of chronic pain. Two recent seminal clinical trials have established its superiority to usual care for the treatment of chronic low back pain (CLBP). However, one key issue remains: minimal clinical difference is found between verum acupuncture (VA) and placebo acupuncture (PA). Meanwhile studies in animals and healthy human models reveal distinct central mechanisms for VA and PA. However, little work has been done to translate the findings from healthy human models to chronic pain conditions such as CLBP. Our aim is to focus on elucidating mechanisms by which acupuncture exerts its therapeutic effects above and beyond the placebo effect. Dysregulation in central pain and emotional processing is increasingly recognized as a key contributor to the pathogenesis of CLBP. Works from others and our group show that acupuncture exerts therapeutic influence in the same central processes as those involved in the pathogenesis on CLBP. These processes include central pain modulation and emotional regulation. In addition, expectations of benefit has also been shown to be an important mediator of response to acupuncture. We hope to delineate the common and differential mechanisms of VA and PA in the CLBP by characterize their effect on the aforementioned biological and psychological factors. In a series to two innovative designs, we plan to a) isolate and elucidate the unique mechanism of VA among those who have NOT responded to PA;b) compare the mechanisms of VA and PA by randomizing those who HAVE responded to either VA or PA. The specific mechanisms that we will study are mechanisms of pain facilitation and inhibition, mechanisms involved in emotion regulation that are known to modulate the pain experience, and the role of expectancy.